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Re: tiny-armed theropods

Matthew Martyniuk <martyniuk@gmail.com> wrote:

> How is abandoning Troodontidae, which is currently used universally in
> the literature, better for stability than re-instating Deinodontidae?
> Some people seem to be arguing that it's better to conserve whatever
> names are currently in vogue in the name of stability. Others seem to
> be saying we should chuck widely-used names if their types are
> dubious, lost, etc. AFAIK nobody is arguing that the phylogenetic
> position of _T. formosus_ is so unstable that (Troodon > Passer) and
> (Saurornithoides > Passer) are potentially different clades.

Briefly.... if _Troodon formosus_ becomes a nomen dubium, the name
will be limited to the holotype: a single tooth.  So what's the big
deal?  I'm glad you asked.  If you carry out a phylogenetic analysis
to determine the affinities of Troodontidae, you'll need to put
_Troodon_ (= a single tooth) into the analysis.  But if _Troodon_ is
an invalid genus (i.e., not a valid operational taxonomic unit, or
OTU) this would be pointless.  Nevertheless, you'd have to stick
_Troodon_ in the analysis just for bookkeeping reasons, to determine
what is captured by _Troodon > Passer_.

All this could actually lead to instability - owing to inadequacy of
the _Troodon_ type, which could mean it may not have a stable position
in the tree.  This problem would not arise with _Saurornithoides_ - or
at least, not nearly to the same degree.

Of course, all this could be alleviated by establishing a neotype for
_T. formosus_.